1. Field of the Invention
This invention generally relates to a shock absorber having a piston, which piston is equipped with damping valves and is fastened to a piston rod. The piston divides the work cylinder into two work chambers filled with damping medium, whereby, parallel to the damping valves there is a bypass connecting the work chambers. The bypass is constituted by a longitudinal hole and a transverse hole in the piston rod located above the piston. There is an axially-movable control rod in the cavity of the piston rod.
2. Background Information
German Patent No. 3 940 290 discloses a shock absorber in which the piston is fastened to a piston rod and is equipped with damping valves. The two work chambers are connected by a bypass parallel to the damping valves, whereby there is a transverse hole in the piston rod above the piston, and the piston rod has a longitudinal hole, the passage cross section of which is actuated by a pilot valve, possibly even a relay valve or a spool valve. One disadvantage of such a configuration is that a drive device is located inside the piston rod and inside the shock absorber, and therefore has to contend with specified space requirements. A further disadvantage is that the seal of the pilot valve on its circumferential surfaces creates problems and causes a large amount of friction if the tolerances are too tight.
German Laid Open Patent Appln. No. 3 535 287, and German Laid Open Patent Appln. No. 3 830 343 disclose shock absorbers with bypass connections, in which the bypass is located outside the work cylinder, and a corresponding drive device is attached laterally to the outer tube of the shock absorber.